1. Field of the Invention
This invention relates to steam turbine systems, and in particular, to a reheater system for providing steam within an appropriate temperature and pressure range for use in turbine rotor gland seals.
2. Description of the Prior Art
Gland seals are utilized to provide an effective seal interface arrangement between a rotating and a stationary element and are most commonly utilized in the steam power generation art to provide seals between a rotating shaft and a stationary steam turbine housing. A gland seal in a turbine apparatus utilizes a quantity of pressurized steam to prevent leakage of steam from within the turbine apparatus to atmosphere or to insure no leakage of atmosphere air past the seal and into the turbine housing.
Whatever the particularized application, however, it is well known that steam utilized in the gland seals in a steam turbine apparatus should be within a predetermined temperature and pressure range. This is required since exposure of the elements of the turbine apparatus to extreme temperature differentials could lead to metal fatigue and premature failure.
Analytical investigation has determined, for example, that steam used for gland seals should be within 300.degree.F of the turbine metal. Repeated use of steam having temperature differentials in excess of this standard causes severe metal fatigue which could result in premature failure.
In the prior art, where turbine apparatus is used for fossil fueled power plants, it is usually a simple matter to lower the temperature and pressure of the steam used in the glands. However, where steam required for utilization in the glands must be increased in temperature, the problem becomes more difficult. The prior art discloses several methods for increasing the temperature of steam used in the gland seals such as heaters using electric heating elements, but no efficient and effective method is available that is also economical.
It is desirable, therefore, to provide an effective, economical system whereby steam used in the gland seals for a turbine apparatus can be provided having both the requisite temperature and pressure needed for the gland use so that damage to the glands and the turbine metal is avoided. In addition, it is imperative that an efficient, economical system to provide steam for glands at temperatures required for either hot or cold starts be available.